Last night I was adding an embedded signup form to a Genesis install. I copied my form action from MailChimp and pasted it into my Genesis eNews Extended Widget. Upon testing, I was getting a Page Not Found error.
After a couple of minutes of staring at the code, I noticed the MailChimp Form Action section is missing the http: it use to have. I inserted http: right before the two forward slashes you see in the pic and my Page Not Found issue went away.